Updated my 5.0 box to 5.1 to fix the auto start problem with the free version. Well now I get PSOD's awesome.
Going for a reinstall + keep datastore this time to see if it fixes it. If not back to 5.0 I guess.
If you end up doing the reinstall with maintaining the datastores, it generally seems to work fine. My son actually fubared my home ESX box by powering my UPS up and down, up and down, up and down because he liked the blue light.
Actually killed ESXi, though my Drobo, Ubuntu 12.04, and Windows XP boxes survived. Reinstalling 5.1 but keeping the DS's worked.